1. Field of the Invention
This invention relates to an improved exhaust system for an internal combustion engine and to a method of operating the same, this invention also relating to an improved burn-off means or unit for such a system or the like and to a method of making such a burn-off means or unit.
2. Prior Art Statement
It is known to provide an exhaust system for an internal combustion engine which burns a hydrocarbon fuel mixture and which produces a carbonaceous particle carrying exhaust gas stream that passes through a filter means of the system that retains at least part of the particles therein, the system having burn-off means for periodically burning the retained particles in the filter means to tend to periodically clean the filter means of the retained particles thereof. The burn-off means has means for raising the temperature of the exhaust gas stream intermediate the engine and the filter means to raise the temperature of the filter means to a particle burning temperature thereof.
One such prior known exhaust system is believed to utilize part of the hydrocarbon fuel mixture for the engine as a fuel to be injected and burned in the exhaust gas stream intermediate the engine and the filter means to raise the temperature of the filter means to particle burning temperature thereof. For example see FIG. 18 and pages 90 and 91 of the article "Particulate filters: a `must` for light-duty diesels?" of pages 78-91 of the March 1981, Automotive Engineering magazine. The source of fuel for such burner is not disclosed in such article but is believed to be the same fuel that is utilized for the internal combustion engine that produces the exhaust gas stream being filtered and that the fuel is fed under pressure into the burner by an atomizing nozzle.
Another such prior known exhaust system utilizes an electrical heater means in the exhaust gas stream intermediate the engine and the filter means to raise the temperature of the filter means to a particle burning temperature thereof. For example, see the U.S. Pat. No. 4,211,075--Ludecke et al, wherein it appears that an electrical heater in the exhaust system thereof is disposed intermediate the engine and the filter means to raise the temperature of the exhaust gas stream being directed to the filter means to assist in the cleaning thereof, such exhaust system also controlling the amount of fuel air mixture being directed to the engine to control the temperature of the exhaust gas stream that leaves the engine and is directed toward the filter.
Another prior known means for controlling the amount of exhaust gas stream being directed to a filter to effect the cleaning thereof is set forth in the U.S. Pat. No. 4,217,757--Crone, wherein it appears that in the exhaust gas recycling system thereof, means are provided for controlling the amount of exhaust gas being passed over a filter means to control the temperature thereof.
During the development of the exhaust system of this invention wherein the applicants were aspirating the fuel mixture into the exhaust gas stream, another, who is not considered as a joint inventor of this invention with the applicants, suggested that a catalyst might be used to ignite the fuel injected into the exhaust gas stream but did not suggest any structure for so accomplishing such feature. Thereafter applicants through various attempts invented the unique arrangement illustrated in FIGS. 1 and 2 of this application wherein a catalyst bed is successfully utilized to ignite the fuel aspirated into the exhaust gas stream.